With regard to a smart ignition system in which an engine is started by means of conduction of an ignition switch due to operation of a push button provided that ID code coincidence is found by intercommunication of ID codes executed between a vehicle and a portable device, a switch device in which, for an emergency when an ID code is no longer transmitted from the portable device due to exhaustion of a battery of the portable device, an electromotive force is generated in a transponder by means of transponder drive radio waves outputted from a coil antenna as a result of placing the portable device in the vicinity of the push button to thus make the transponder output an ID code, is known from Patent Document 1.